Coupling arrangement for an oscillatory system



Feb. 17, 1959 c. E. ELLSWORTH COUPLING ARRANGEMENT FOR AN OSCILLATORY SYSTEM 3 Sheets-Sheet 1 Filed Sept. 28, 1953 Feb. 17, 1959 c. E. ELLSWORTH 2,874,357

COUPLING ARRANGEMENT FOR AN OSCILLATORY SYSTEM Filed Sept. 28, 1955 N s Sheets-Sheet 2 Feb. 17, 1959 C E, swoR H 2,874,357

' COUPLING ARRANGEMENT FOR AN OSCILLATORY SYSTEM Filed Sept. 28, 1953 3 Sheets-Sheet 3 I IIII'IIIIP'IIIIIIIII". II'IIIIIIIIIII I I I I I I I I I n I I I I I I l I I l I I I I l I I I I I I I I I I I I I u I United States Patent COUPLING ARRANGEMENT FOR AN OSCILLATORY SYSTEM Carl E. Ellsworth, Anchorage, Ky., assignor to Chemetron Corporation, a corporation of Delaware Application September 28, 1953, Serial No. 382,525

6 Claims. (Cl. 333-27) This invention relates to high-frequency oscillator systems such as used, for example, in dielectric heating and more particularly to an inductive-coupling arrangement for reentrant cavity oscillators which aifords the wide range of adjustment required to meet the widely different conditions encountered in dielectric heating.

In, accordance with the present invention, the coupling arrangement is comprised of a coupling loop having a shorting member or vane pivotally mounted for movement in an arcuate path throughout which opposite sides of the vane are in contact with opposite sides of the loop. Thus, as the vane is moved about its axis, the effective perimeter of the loop is varied so to change either its self-inductance, or the mutual inductance or coupling between the loop and an associated industive element such as the fin or leg of a reentrant cavity applicator, or to change both the aforementioned self-inductance and the mutual inductance. The pivotal axis of the shorting vane is disposed substantially out of the path of the high circulating currents so that for all positions of the vane substantially all the loop current flows through a portion of the shorting vane which is in contact with the sides of the loop and not through the structure which provides the pivotal mounting for the 'vane.

More particularly the preferred couplingloop, which 7 is adapted for accommodating high intensities of highfrequency circulating currents, includes at least two wide substantially parallel sides. One dimension of the shorting vane corresponds with the spacing between the sides of the loop, and the other dimension of the vane approximates the length of the loop so to provide engagement of two opposite sides of the vane respectively with the wide sides of the loop throughout the wide range of angular adjustment of the shorting vane.

In another aspect'of the present invention the shorting vane is movable to change the self-inductance of the coupling loop while the mutual inductance or coupling between the loop and the associated inductive element is maintained constant.

In yet another aspect of the present invention, the shorting vane is comprised of a plate member which, in shorting out a portion of the coupling loop, effectively shields the shortcircuited portion to minimize inductive, interaction between the shorted and non-shorted portions of the coupling loop.

2,874,357 Patented Feb. 17, 1959 ICC ' Fig. 4 is an enlarged perspective of a preferred form of the shorting vane or bar;

Fig. 5 is a sectional view of the shorting vane taken along a line substantially corresponding to line 5-5 of Fig. 4;

Fig. 6 is a perspective view of a portion of one type of coupling loop embodying the present invention for varying the self-inductance of the loop without substantial change in mutual inductance or coupling between the loop and an associated inductive element; and

Fig. 7 is a perspective view of a coupling loop embodying the present invention in which the axis of rotation of the shorting vane is parallel with the flux lines linking the loop.

Referring to Fig. 1, there is illustrated in schematic form a coupling loop 10 embodied in a dielectric heating applicator 11 of the reentrant cavity type generically similar to that described and claimed in Warren application Serial Number 138,628, filed January 14, 1950, abandoned in favor of Warren application Serial No. 419,633, filed March 26, 1954, now Patent No. 2,783,344. In the particular embodiment illustrated, the applicator 11 is comprised of a metallic housing 12 within which the dielectric workto be treated is disposed for heating by the high-frequency electric field established between an upper electrode 13 and a lower electrode 14 which may be the lower wall of housing 12, a raised platform, or in some instances a conveyor. The upper electrode 13 is connected to the lower free end of the-metallic inductor or fin 15 whose upper end is connected to the top wall of the housing 12. Usually, flexible conductors are included in the fin-electrode assembly 13, 15, as between electrode 13 and the adjacent end of the fin 15, or as shown between the top wall of the housing 12 and the adjacent end of the fin 15 to permit raising and lowering of the upper electrode 13. The inductance of fin 15 provides the lumped inductance of a heating circuit resonated by the capacity between the heating electrodes. The high-intensity, high-frequency magnetic field of fin inductor 15 traverses the coupling loop 10. The current return path between the upper end of the fin 15 and the lower electrode 14 is provided by the wall structure of the housing 12 and is of negligible impedance. The resonator thus formed is inductively coupled by loop 10 to the anode of an oscillator tube (not shown) to provide an oscillator system generically similar to those disclosed and claimed in the aforesaid Warren applications.

In dielectric heating applicators, variations in electrical and/or physical characteristics of the load occur during a heating cycle. Such variations in load change the operating characteristics of the applicator and may result in damage to the load, overloading of the dielectric heating unit, damage to one or more components such as the oscillator tube, or lowering of the heating. rate. It usually is necessary or desirable, therefore, to make compensatory changes of proper sense and magnitude to off-set the effect of such changes of the load characteristics to reestablish desired operating conditions in the applicator.

In general, such compensatory change may be effected by changing the mutual inductance or coupling between the loop 10 and the inductor or box-like fin 15, or by changing the self-inductance of the loop, which latter changes the natural frequency of the loop, or by changing both the aforementioned mutual inductance and the self-inductance. Various compensating arrangements for varying one or more of such parameters are disclosed and claimed in the aforesaid Warren application and in Warren applications Serial Nos. 419,072, 419,073 and 419,074, all filed March 26, 1954, now respectively Patents Nos. 2,783,346, 2,783,345 and 2,783,347, and in copending applications, Carl E. Ellsworth, Serial Number 263,599, filed December 27, 1951, now Patent No.

i the opposite sides 22 and 23 of the loop and functions as a short-'circuiting device between the sides.

In the particular loop construction shown in Fig. 1, the copper pipes 16, 17 for supplying coolant to the anode of the oscillator tube (not shown) serve as a form for the electrically conductive sheet 18. Ends 16A, 17A of the pipes, electrically connected to wall 12A of the applicator housing, serve as a ground connection for one end of the loop. The other ends 16B, 17B of the pipes pass through insulators 19 in housing wall 12A for connecting the other end of loop to the anode of the oscillator tube. When as shown in Fig. 1, the loop sheet 18 is on the outside of the loop form provided by pipes 16, 17, there are preferably added, as discussed in connection withFig. 2, supplemental sheets connected to the inside of the loop form for contact by opposite sides of vane 20.

As the vane 20 of Fig. l is moved about its pivotal axis and within the perimeter of the loop 10, the percentage of the electromagnetic field linked by the loop is varied so to change the coupling between the loop and the inductor 15. With the vane 20 in its horizontal position (Fig. 1), preferably as close to the top of the loop 10 as possible, the effective area of the loop is maximum and linkage by the loop of the flux produced by current in the inductor is a maximum. As the vane is moved progressively downwardly, as illustrated by dotted lines, toward an ultimate vertical position, the linkage decerases to a minimum value due to more and and more of the area I of the loop 10 being shorted out. The decrease in percentage of fiux linked by the loop will cause a decrease in the mutual inductance or coupling. At the same time, as the vane 20 is moved downwardly the effective length of the loop is decreased, which decreases the self-inductance of the loop and raises its natural frequency. When operating in the supra optimum coupling range, both the decrease in coupling and the increase in natural resonant frequency of the loop have the effect of increasing electrode voltage. vFor an explanation of supra optimum coupling, reference may be had to the aforementioned Warren and Wilson applications.

The shape and dimensions of the shorting vane 20 are determined by the internal configuration of the loop 10 and the range of coupling desired. More specifically one of the dimensions of the vane 20 is such as to provide for engagement between two opposite sides of the vane and thesides 22 and 23 of the loop 10 throughout the range of arcuate adjustment of the vane. For the maximum range the vane 20 should have a dimension, normal to its pivotal mounting, substantially equal to the distance be- .tweenthe upper and lower portions of the loop, i. e. the

length of the loop.

Inductive interaction or coupling between the shorted and unshorted portions of loop 10, and between the shorted portion of the loop and inductor 15 is minimized by providing, as in Fig. 1, that the shorting vane 20 shall shield the shorted portion of the loop from linkage with the electromagnetic fields of the unshorted portion of the loop and of the inductor. Accordingly, the preferred embodiments of the present invention afford a greater range of electrode voltage variation than heretofore attained with couplingloops of the fixed type having shorting arrangements which-do not shield the shorted portion of "the-loop. In-these other types of shorting arrangements,

4 as shown and claimed in said Warren applications, there is present an inductive interaction between the shorted and unshorted portions of the coupling loop. This is analogous to the interaction between shorted and unshorted turns of a coil which, as is well known, will cause the overall inductance of the coil to decrease due to the field produced by the current in the shorted turn being out of phase with the field produced by the unshorted portion of the coil. Such decrease in inductance will cooperate with the decreased coupling between the unshorted portion of the loop and the fin inductor so as to increase the range of variation of the electrode voltage. However, without the shielding effect afforded by the preferred embodiments of the present invention, the shorted portion of the coupling loopvwill also be subject to linkage by the electromagnetic field of the fin inductor, and as the perimeter of the unshielded shorted portion increases, the coupling between that portion and the fin structure would increase accordingly. This latter may be of greater effect upon electrode voltage than the effect of the decrease in inductance of the loop caused by the interaction between the unshielded shorted and unshorted portions of the coupling loop. Hence the range of electrode-voltage variation with previous unshielded shorting arrangements is less than that obtainable with the shielded, shorting arrangement of the preferred embodiments of the present invention.

The improved operation afforded by the shielding effect above described is accomplished in the embodiment of Fig. l by contact of two opposite sides of the shorting vane 20 respectively with the opposite sides of the loop 10 throughout the range of adjustment of the vane, so as to eliminate spaces between the sides of the shorted por tion of the loop through which the electromagnetic field of the inductor 15 could pass to link with the shorted portion of the loop. I

Movement of the shorting vane 20 about its pivotal axis may be effected by any well known device. As exemplary of such a device, there is illustrated (Fig. 1) an external manually operable crank 24 mounted on an end of the shaft 21 which extends through the wall 12A of the housing 12. At least a portion of the shaft 21 should be of insulating material to insulate the crank or knob 24 from the high potential of the loop 10.

In Fig. 2 there is shown in detail a commercial type of variable coupling loop arrangement embodying the present invention. As in Fig. 1, loop 10 is comprised of a framework consisting of a pair of spaced copper pipes 16 and 17 preferably conductively connected by a sheet of material such as copper or the like (for clarity not shown here but similar to the sheet or web 18 shown in Fig. 1) which substantially covers the outer periphery of the pipes to form the single coil loop.

Particularly in those instances where the opposite sides 22 and 23 of the coupling loop 10 are of different widths,

or are of curved configuration, or contain structural ribs or the like, spaced parallel electrically conductive plates 25 and 26 may be added to provide flat parallel sides for more effective contact with opposite sides of shorting vane 20A. The plates 25 and 26 may be of aluminum or like material and mounted in any well known manner respectively on opposite sides 22 and 23 of the coupling loop 10. In Fig. 3 the plate 26 is omitted for clarity. In providing flat parallel sides, the plates 25 and 26 also present a greater area for contact between the shorting vane 20A and the coupling loop 10 throughout the range of movement of the vane to thereby increase the range of variation in mutual inductance and self-inductance of the loop. The shorting vane 20A, Fig. 2, is mounted for arcuate movement within the area defined by the spaced parallel plates 25 and26 by means for the shaft 21 journaled in bearings 2 1A secured on'ends of the plates.

In order to provide improved electrical contact throughout the arcuate movement of the shorting vane 20A, a plurality of resilient contacts 27, Figs, 2-4, may be seeuredon opposite sides =of "thevane :for' engagement with the spaced parallel 'plates25and 26of-ithe coupling loop. Substantially all of the high circulating currents which flowfrom the loop 10 into the'shorting v'ane 20A'will be carriedby the resilient contacts 27 of the shorting vane. Most of the current intercepted by the shorting vane 20A will pass through the vane contacts 27 furthest away from the shaft 21 of the shorting vane20A and, accordingly, at most only a very small portion of the total circulating current will be conductedby the shaft. Thisconstruction obviates the possibility of excessive heating, or even welding, at high resistance points in the shaft structure, such as bearings 21A, etci, which might causethe shaft 21 to bind or freeze. i v i The shorting vane or plate member 20A is shown in detail in Figs. 4 and m be comprised of a framework in cluding spaced longitudinal members 30 and laterally spaced reenforcing struts 31, the wholecovered by a skin 32of thin sheet metal. The shaft 21 passes through the vane 20A at one side thereof and is firmly affixed thereto. Contact between the shorting vane 20A and'the inner-sides of the spaced parallel plates 25 and 26 is assured throughout therang e of arcu'ate' sliding movement of the shorting vane by the plurality of resilient loop contacts 27 formed of beryllium-copper straps mounted along the two opposite sides of the vane which extend normal to the pivoted side of the vane. The contacts 27 may be mounted on the shorting vane framework by means of screws or in any other well known manner In the embodiment shown, the shorting vane 20A is rectangular in configuration, complementary to an outline defined by the spaced parallel plates 25 and 26. In embodiments in "which the spaced plates are not parallel, the contacts 27 may be varied in length to conform to the particular configuration, and when the variation is from the top of the plates to the bottom the resilient contacts will deformin accordance with the variation.

For rotation of the shaft 21 of the shorting vane 20A, there is provided a shaft 33 (Figs; 2 and 3) which passes through wall 12A lof the housing and which is connected internally thereof to shaft 21 by an insulated coupling 34.

-'I he coupling BA should have an eifective length sufficient to. insulate the end of shaft 33 from the highv voltages of the couplinga loop, In many embodiments, where-the invention is applied to dielectric heaters of the typeillustrated, the longitudinal length of an insulator is limited by the distance of the coupling loop from the adjacent wall of the applicator housing. To provide the adequate insulation necessary to permit connection of a driving means to shaft'33 at ground potential, the insulated coupling 34 comprises a large sheet of insulating material 35 having mounted on opposite sides thereof pairs of metallic stand-off connectors 36 and 37. The connectors 36 and 37 are respectively connected by metal bars 38 and 39, displaced at right angles to one another, and to which the shafts 21 and 33 are respectively connected. The effective insulation length of this construction is equivalent to a bar of insulating material several times the distance between connecting bars 38 and 39.

The driving means for the shorting vane 20A (Fig. 3) is located exteriorly of housing 12 and is comprised of a reversible motor 40 whose motion is transmitted to the shorting vane 20A byway of sprocket and chain drive 41,

. shaft 42, sprocket and chain drive 43,- gear-reduction box screws 46A and47A respectively. The deenergization of motor 40 at predetermined limits of travel of shorting 7 vane 20A is controlled by switches 50-and 51, which may be of the .microswitch type.

The switch 50 includes a member 50A engageable by a forward inclined surface of cam 47 to open-the power circuit of motor 40 and halt the upward travel of the shorting vane 20A. Thelower limit of travel of the shorting'vane 20A is. controlled by micro-switch 51 whose memberSlAis operated by a forward inclined surface of cam 46. The switch' operating cams 46 and 47 may be adjusted so as to vary the upper and lower limits of travelof the shorting vane. To this end the earns 46 and 47 are slotted and made adjustable relative to their respective thumb screws 46A and 47A. The travel of .nut 45A may be further limited by fixed mechanical stops (not shown) just beyond the range of adjustment of the limit switch cams. V

In the modification shownin Fig. 6, coupling loop 103 is comprised of two sections oneof which has an area 60 threaded by magnetic flux moving in a direction indicated by the arrows and the other of which has an area .61 which is so oriented that it is not threaded by any. appreciable amount of the magnetic flux. The horizontal portion of the coupling loop 10B is provided with a pair of spaced parallel vertically disposed plates 25B and 26B serving functions similar to that of the plates 25 and 26 of Fig. 2. The shorting vane 20B, similar to vane 20 of Fig. 1, is in slidable contact with the spaced parallel plates along the entire coextensive portions thereof.

Resilient contacts, not shown, but similar to contacts 27 of Fig. 2 may be added to the sides of the vane 20B for improved electrical contact between the plates 25B and 26B and the vane.

Movement of the :shorting vane 20B about the axis of shaft21B will vary the inductance of the coupling loop 103 and hence change thenatural'frequency of the loop. Inasmuch as the area 61 of the couplingloop 10B is not linked by the magnetic flux movement of the vane 20B will. not appreciably change the coupling between the loop and an associated inductor a (not shown). However, change in the 'natu'ralifrequency of the coupling loop 103 will effect a change. in the electrode voltage in manner described in the aforesaid Wilson application and therefore the arrangement provides compensation of substantial range for changesin load characteristics. 7

Movement of theshorting vane 20B about its axis may be effected by any well known device. For illustrative purposes there is disclosed a manual driving device similar to that illustrated in Fig. 1 wherein a crank 24B is mounted on the shaft 21B.

In Fig. 7 there is illustrated another modification of the present invention wherein a coupling loop arrange ment includes a shorting vane 20C having only one side in slidable electrical contact with a side of va coupling loop 10C. The shorting vane is pivotally mounted on a side 22C of the loop by means of a shaft 21C extending parallel with the lines of flux moving in a direction indicated by arrows. The mutual inductance between the coupling loop 10C and an inductor similar to inductor 15 of Fig. 1 is varied through movement of shorting vane 20C from an upper vertical position where the self-inductance of the. loop, the mutual inductance and coupling of the loop and inductor are at a maximum,-to a lower vertical position where the aforesaid self-inductance, mutual inductance and coupling are at a minimum.

The coupling loop 100 may be rectangular in configuration similar to that shown in Fig. 1. However, as illustrated side 23C of the coupling loop is of arcuate configuration to enhance the range of variation of self-inductance and mutual inductance by permitting rotation or pivotal movement of the shorting vane through-an arc' of approximately Good electrical contact between the vane 20C and the loop 100 is assured by the provision of plate 25C mounted on side 23C of the loop and the addition of resilient contacts 27C on the adjacent side of the shorting vane. The plate 25C may extend completely around .the inside of-the. loop 100 in mu'chthe same manner and :forlthe samepurpose-as sheet..18 -which' covers theoutside of the loop 10 (Fig. 1).

Movement of the-shorting vane20C. may be effected by -way of a crank 24C mounted 'exteriorly of the applicator housing and mechanically connected totheshorting vane 20C-through shaft 33C,.bevel gears 62, 63 and shaft 21C. ,A portion -of one of the shafts 33C, 21C, like shaft 21 (Fig. 1), isrnade of .insulating materialtomaintain the crank 24C at ground. potential.

Passage throughthe .shaft' structure 21C of high-frequency, high-intensity currents which circulate in the loop is avoided by -a distribution of such currents through a plurality of resilient-conductive straps 64 fastenedto-upper and lower surfaces of the shorting vaneand the side 22C of thecouplingloop. The: straps 64serve as short-circuiting 'members permitting the currents to by-pass the 'shaft'structure. .Inthis modification, the shorting vane -coupling loop having substantial width and length, said loop having a. substantial portion of at least two sides formed of conductive sheet. metal, means for varying the effective coupling area of said loop by moving lengthwise ofrsaid loop anelectrical connection extending from one sheet metal .side of saidloop-ata location adjacent one .end ofsaidloop to the other sheetmetalside'thereof to .move progressively along and lengthwise of at least one sideof said loop' thecurrent path between .opposite sides thereof, said means'comprising'a shorting plate member which extends across :said "width of said loop, and-the edge-portions thereof forming said electrical connection from said one sheet metal side of said loop to said other sheet metal side thereof, and means pivotally mounting said shorting plate member at oneend thereof for rotation of said shorting member within and relative to said loop from said positionclose to said one end through z'anaarcuateitravelc-pathrforvmovi-ngfsaid ielectricali'connection 'tOFShO1'.tI1' said current path.

i -2..- The ="adjustable coupling arrangemcntof claim I in iwhich onezside of said loop has an 'arcuate configura- .tion' andrin whichtsaid shorting plate member is pivoted about. an axis: parallel withthe axis of the arcuate portion .of saidloopwiththe opposite end of'said shorting member movable along. thearcuate portionof said loop from a positionadjacent one end of :the loop toward the oppositenend. of the loop 'to' vary-;the eflective perimeter length of said loop.

3. The coupling arrangement of claim 1 in which the axis of rotation of said shorting plate member is normal to the planes which respectively include the sheet metal forming the respective sides .of said loop.

4. The adjustable coupling arrangement of claim 3 in which-said pivotal mountingzmea'ns is carried by .said loop andin whichsaid shorting plate member has a length which takennormalto the axis of its mounting means is approximately equal to ,said length of said loop. 5. The coupling arrangement of claim 1 in which the portion of said loop including said conductive sheet metal is disposed at right angles to the-plane of the remaining .portion of said loop, said pivotal mounting means being located adjacentone end of said loop for rotation of said shorting plate member between the sheet metal portions thereof, whereby the inductance of said loop may be varied byrotating said shorting plate member to change the length of said loop without variation of fiux passing through said remaining portion of said loop.

6. The. adjustable coupling arrangement of claim 1 in which-saidshorting platemember comprises spaced walls of-thinsheetmetal reinforced by spacing struts and having along oppositeedges thereof a plurality of resilient loop contacts, which loop contacts engage said thin sheet metal to form said electrical connection between said sheet metal sides.

"References Cited in the file of this: patent UNITED STATES PATENTS 2,373,233 Dow tal. Apr. 10, 1945 1 2,498,529 Clark Feb. 21, 1950 2,617,853 Gilmer' NoV .'11, 1952 2,693,582

'Skar Nov. 2, 1954 

